Caravan Guy said:
Under the van, it appears the front drive shaft has hit the frame. Tried using crowbars to make it move, so such luck. Ted had a similar problem, but mine was intermitent. Drive a bit, then all fo a sudden, the shaft hits the bottom of the van. I think Ted shimmed up the front mount and pretty much solved his problem. My front mount is not good, the left engine mount is weak. Will replace and see what happens. Carquest does not have them, so NAPA is my next stop.
I did shim but I still have the problem, however it only appears under heavy accelleration (which I can easily avoid) In my case my frame is bent so there is nothing more I can do (except take it to a frame shop) and the front mount is shimmed as much as possible, also I put a bolt in the front mount above where the normal bolt goes, in order to prevent the front mount from compressing as much as it normally can.
Unfortunately, the aftermarket engine mounts are no good here, they use softer rubber and will compress more than the OEM mounts, making the problem worse.
The way the geometry works is this:
On accelleration, the resistance of the front 2 axles tends to force the front of the engine up, and the back of the engine down. The 2 side mounts are a bit behind the centerline of the engine, so what happens is when all the mounts compress the back of the engine will go down.
If all mounts are stiff and fresh, and the engine cradle is aligned, the compression of the mounts is not enough for the driveshaft to touch the bottom crossmember. When the driveshaft touches it transmits all the vibration in the engine to the chassis and the body amplifies it, and it sounds like someone is sawing at the body with a dozen files. Worse, the second the driveshaft is slapped against the bottom crossmember it imparts a twisting force on the engine which pulls weight off one of the front wheels, causing it to slip, as soon as the wheel slips the powertrain unloads and the shaft snaps back up off the crossmember, whereupon the wheel reloads and the cycle starts over again. You end up getting massive wheel hop, bang, bang bang bang bang.
If the mounts get weak the compression is enough for this to happen on heavy accelleration. The worse the mounts get the more this happens.
You can shim the front mount with washers about a half inch. You can shim the side mounts with washers a bit less than a quarter inch. Shimming the front mount pushes it down, shimming the side mounts push them up. Start by shimming the side mounts with a single washer on each bolt hole and see if it stops. Then start adding washes to the front mount, testing each time, until it either stops or you run out to the end of the bolt.
If you have to replace mounts, get the stiffest ones you can find. The front is the critical one.
Ted
